9.6

CVE-2026-100818: mozilla firefox Use After Free

CVSS: 9.6v3.1CriticalAnalyzed
AliasesUBUNTU-CVE-2026-100818DEBIAN-CVE-2026-100818
Published 29-09-2026Last modified 30-09-2026
Open JSON

Vulnerability summary

CVE-2026-100818 is a critical (CVSS 9.6) Use After Free vulnerability in mozilla firefox. EPSS estimates a 0.26% chance of exploitation in the next 30 days, higher than 16.5% of scored vulnerabilities.

Overall risk
70/100
0100
High · default modelHow is this calculated?
CVSS score
9.6/10
010
Critical · v3.1 (CVE.org)
EPSS score
0.26%
0%100%
Low · Change unavailable
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 10 · Related 8
MGASA-2026-0491MGASA-2026-0492OPENSUSE-SU-2026:11917-1OPENSUSE-SU-2026:12097-1OPENSUSE-SU-2026:12098-1OPENSUSE-SU-2026:21980-1

Timeline

  1. 29-09-2026
    PublishedVulnerability first disclosed.
  2. 30-09-2026
    Last modifiedVulnerability information updated.

Description

Sandbox escape due to use-after-free in the Widget: Gtk component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, and Firefox ESR 140.17.

CVSS metrics

4 scores · 4 sources · 1 version

EPSS trend

Probability

0.26%

Chance of exploitation in the next 30 days

Percentile

17%

Versus all other CVEs

30-day change

Change unavailable

Change unavailable

30-09-202619-10-2026
EPSS score
0.26%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Ubuntu8 products
  • mozjs102All versions (No fix recorded)
  • mozjs115All versions (No fix recorded)
  • mozjs38All versions (No fix recorded)
  • mozjs52All versions (No fix recorded)
  • mozjs68All versions (No fix recorded)
Debian2 products
  • firefox-esr< 153.4.0esr-1~deb12u1 | < 153.4.0esr-1~deb13u1 | < 153.4.0esr-1
  • thunderbird< 1:140.17.0esr-1~deb12u1 | < 1:140.17.0esr-1~deb13u1 | < 1:153.4.0esr-1
Mozilla2 products
  • firefox< 140.17.0 | ≥ 141.0, < 153.4.0 | ≥ 154.0.0, < 157.0.0
  • thunderbird< 140.17.0 | ≥ 141.0, < 153.4.0 | ≥ 154.0, < 157.0

3 vendors · 12 products

References

12 links
Show all 12 references